1. Field of the Invention
The present invention relates to a high voltage switch circuit of a semiconductor device, and more particularly to, a high voltage switch circuit of a semiconductor device which can efficiently switch a high voltage in a low voltage.
2. Discussion of Related Art
In general, a semiconductor device requires a pumping voltage higher than an input power voltage, and also requires a high voltage switch for switching the high voltage.
FIG. 1 is a circuit diagram illustrating a conventional high voltage switch circuit.
Referring to FIG. 1, the conventional high voltage switch circuit includes a NAND gate NG1 for outputting a pumping clock signal P_CLK according to an external enable signal EN and a clock signal CLK, a pumping unit 10 for outputting a pumping voltage Vpump according to an external first high voltage Vpp and the pumping clock signal P_CLK, a precharge unit 20 for precharging the output from the pumping unit 10 according to the enable signal EN, and a switch unit 30 for switching a second high voltage Vin according to the pumping voltage Vpump of the pumping unit 10.
The pumping unit 10 includes a first capacitor C1 coupled between a pumping clock signal input terminal and an output terminal of the pumping unit 10, an inverter 11 and a second capacitor C2 connected in series between the pumping clock signal input terminal and a first node Q1, a native first transistor T1 coupled between the first node Q1 and the output terminal of the pumping unit 10 and driven according to the first node Q1, and a second transistor T2 coupled between the first node Q1 and an external high voltage input terminal and driven according to the output terminal of the pumping unit 10.
The precharge unit 20 includes a third transistor T3 coupled between an enable signal input terminal and the output terminal of the pumping unit 10 and driven according to a power supply voltage Vcc. The switch unit 30 includes a fourth transistor T4 coupled between a second high voltage input terminal Vin and a second high voltage output terminal Vout and driven according to the output from the pumping unit 10.
The operation of the conventional high voltage switch circuit will now be explained.
When the enable signal EN has a logic high level, the output terminal of the pumping unit 10 is precharged by the third transistor T3. Here, the output value from the NAND gate NG1 is varied by the clock signal CLK, and inverted by the inverter 11. The pumping voltage Vpump is generated through a positive feedback loop comprised of the first and second capacitors C1 and C2 and the first and second transistors T1 and T2. However, threshold voltages of the first and second transistors T1 and T2 causing a voltage loss of the positive feedback loop are increased due to a back bias voltage in the conventional high voltage switch circuit, so that there is a problem that the conventional high voltage switch circuit is not appropriately operated in a low voltage of below 2.5 V.